applying fuel gas welding (fgw) processes and...

Applying Fuel Gas Welding (FGW)Processes and Techniques

UNDER A SPECIFIC HEAT PROCESS, two pieces of materialcan be fused or joined together. This is the principal

function of welding. Metal is commonly used in thewelding process. However, other materials, such asplastics, can be welded. Materials are fused togetheronce a melting point is achieved. The bond is completedas the materials cool. The bond will be as strong as theoriginal material if the process is accomplished properly.

Objective:

� Explain the fundamentals and techniques offuel gas welding.

Key Terms:

�

Understanding Gas Welding

Several forms of gases will burn. Acetylene and propane are commonly used for heating,

cutting, and welding metals. These gases are compressed and are stored in cylinders. The fun-

damentals and techniques available for fuel gas welding allow for using the gases safely. The

process is built upon two fundamental principles. Acetylene burned with oxygen produces a

flame so intensely hot that it can be used to melt and fuse metals. A stream of oxygen directed

against a piece of iron or steel, which has been heated to its kindling temperature, causes the

metal to burn away so it can be used to cut or shape the metal as desired.

FUEL GASES

Acetylene, C2, H2, is a fuel gas made of carbon and hydrogen that is produced from the

chemical reaction between calcium carbide and water. Acetylene is colorless, but it has a dis-

E-unit: Applying Fuel Gas Welding (FGW) Processes and Techniques

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acetylene

blowpipe

carburizing flame

flash arrestors

flashback

neutral flame

oxidizing flame

oxygen

regulator

tinct odor. The flame produced by acetylene can generate a theoretical temperature of 6300°F

and a measurable temperature of 5800°F. It is stored in a free state under pressure greater than

15 psi.

Methylacetylene propadiene (MAPP) is a stabilized methylacetylene. It combines the high

energy characteristics of acetylene with the handling and storage features of liquefied petro-

leum gases. MAPP gas is more stable than acetylene, making it safer. C3H4 has a flame tem-

perature of 5300°F. The bushy flame makes welding difficult with MAPP gas.

Propane, C3H8, has a maximum flame temperature of 5300°F. The volume of oxygen

required for that temperature produces an oxidizing flame unacceptable for iron and steel

welding.

Oxygen

The oxygen used in the oxyacetylene process is manufactured from liquid air and is stored

in hollow steel cylinders. Oxygen is a nonflammable, tasteless, colorless, and odorless gas that

is slightly heavier than air. When combined with other elements, it will support combustion.

Commercial oxygen is supplied to users in seamless steel cylinders charged with oxygen to a

pressure of about 2200 psi at 70°F. The pressure will increase and decrease as the temperature

changes. The oxygen cylinder has a valve made of tobin bronze. Since bronze is soft, protec-

tion must be provided to prevent it from being broken or knocked off.

EQUIPMENT AND SUPPLIES

Several pieces of equipment are used for fuel gas welding. Cylinder tanks, regulators, hoses,

and an appropriate torch provide a basic framework. The equipment should be provided in

good condition and from a reliable dealer who guarantees service on all equipment and

supplies.


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BROADENING AWARENESS…

AMAZING ASPECTS: Be Safe

Because of the intense heat and other opportunities for accidents, safety is of extreme

importance in fuel gas welding. This form of welding can cause metal to spark, drop, or fly. As a

result, serious injuries can occur. The following are some suggested practices for proper protec-

tive clothing.

• Wear goggles or a face shield approved for fuel gas welding.

• Wear leather welding gloves when welding or cutting. Do not touch hot metal with gloves.

• Wear protective clothing, such as material that will resist flames and heat.

• Wear leather shoes that will resist burns and provide protection from heavy pieces of

metal.

Oxygen and acetylene fittings are

not interchangeable. Oxygen fittings

have right-handed threads, while

acetylene fittings have left-handed

threads or a smaller size right-hand

connection. A regulator is attached

to each of the tank valves. A regula-

tor is a device used to vary line pres-

sure on a tank. Each regulator has a

diaphragm adjusting screw to vary

the line pressure and two gauges:

one showing cylinder pressure and

one showing line pressure.

The hoses used are colored: one

green and one red. The green hose is

used for oxygen and has fittings with

right-handed threads. The red hose

is used for the fuel gas and has left-

handed fittings. The hoses connect

the blowpipe to the regulators. The

blowpipe is a mixing chamber. The two gases are mixed and delivered to the tip ready to

burn. The blowpipe has a valve to control the oxygen and a valve to control the acetylene.

A variety of tips are attached to the blowpipe for different tasks. A welding tip is used for

welding pieces together, and a cutting attachment with a tip is used to cut metal. Special tips

are available to perform other tasks, such as heating.

TABLE 1. Other Pieces of Fuel Gas Welding Equipment

Type of Equipment Purpose

Welding goggles or faceshields

They filter out ultraviolet and infrared rays to protect the operator’seyes. A No. 4 lens should be used.

Friction lighter It is used to light the blowpipe.

Gauntlet gloves They are worn when welding or cutting to protect skin.

Cart Cylinders should be chained in an upright position when used andstored.

Safety caps They should be positioned on top of the cylinders and should not beremoved until the cylinders are secured.

Flash arrestors aredevices that will extinguishany flame that attempts togo through them due to aflashback.

They should be mounted on the oxygen and acetylene lines at theregulators. A flashback is a fire inside the blowpipe. When aflashback occurs in an oxyacetylene unit, flame physically travels upthe welding tip and through one or both of the hoses to theregulator.


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Oxygen pressuregauges

Oxygen cylindershut-off valve

Acetylene pressuregauges

Acetylene cylindershut-off valve

Cart

Chain tosecure cylinders

Acetylene cylinder

Oxygen cylinder

Acetylene pressureregulator

Oxygen pressureregulator

Oxygen hose

Acetylene hose

FIGURE 1. Major parts of an oxyacetylene welding and cutting outfit.

SET-UP

Following proper procedures when setting-up the fuel gas welding equipment will insure

that there are no gas leaks. Therefore, accidents can be minimized and, hopefully, avoided.

General procedures are as follows:

1. Place the cylinders in a cart. Fasten them together with a chain, or fasten the cylinders

in some other manner to prevent them from being tipped over during use or storage. If

an acetylene cylinder is tipped on its side, it should be set upright for at least 30 minutes

before it is used.

2. All oxygen and some acetylene cylinders have iron caps to protect the cylinder valves.

Remove the caps. Stand to one side so you are not directly in line with the tank valves.

“Crack” the cylinder valves slightly. Then close them quickly, which will blow out all

dust and other foreign matter.

3. Connect the acetylene regulator to the acetylene cylinder and the oxygen regulator to

the oxygen tank. It should not be possible to interchange the regulators. To avoid con-

fusion, the regulator with the larger numbers belongs on the oxygen tank.

4. Connect one end of the green hose to the outlet connection on the oxygen regulator

and the other end to the oxygen connection on the blowpipe. Be sure the flash arrestor

is attached to the regulator and the hose is attached to the arrestor. If the unit does not

have a built-in check valve, be sure one is put between the hose and the blowpipe.

5. Connect one end of the red hose to the outlet connection on the acetylene regulator

and the other end to the acetylene connection on the blowpipe. Repeat the flash

arrestor step in the same manner as conducted for the oxygen regulator.

6. Close both regulator valves by turning the regulator diaphragm screw counterclockwise

until the screw is loose. Always close the regulator valves before opening the cylinder

valves to prevent the tank pressure from damaging the regulator.

7. While standing to one side, not directly in front of the regulator, open the oxygen cylin-

der valve slowly. Wait until the cylinder pressure has registered on the high-pressure

gauge before completely opening the valve. The oxygen tank valve is double seated, and

it should be opened completely to prevent loss of the high-pressure oxygen around the

tank valve.

8. Standing to one side, not directly in front of the regulator, open the acetylene valve

slowly. This valve should never be opened more than one turn so it can be shut off

quickly. Always leave the T-wrench on the valve while you are working in case the fuel

gas needs to be shut off quickly.

9. Open the oxygen valve on the blowpipe about one-eighth of a turn. Turn the screw on

the oxygen regulator clockwise until the desired pressure is reached on the oxygen low-

pressure gauge. Close the oxygen valve on the blowpipe.


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10. Open the acetylene valve on the blowpipe about one-eighth of a turn. Turn the screw

on the acetylene regulator clockwise until the desired pressure is reached on the acety-

lene low-pressure gauge. Close the acetylene valve on the blowpipe.

Testing for Leaks

A good shop maintenance practice should include testing for leaks on fuel gas welding

equipment. This practice should be conducted when the equipment is first set up, when cylin-

ders are changed, and when an odor is present (when the equipment is not being used).

Test for leakage by applying soapy water around the valves and connections. If a bubble

appears at a valve or a connection, a leak has been detected. It should be corrected before using

the equipment. It is important to use grease-free soap.

OPERATING

Fuel gas welding requires precise settings on gauges and valves. These settings assist the

operator in achieving proper lighting of the torch and a neutral flame. The correct lighting and

shutting down procedures should be followed at all times.

TABLE 2. Lighting Procedure for Welding or Cutting Torch

Correct Lighting Procedure

1. Place goggles or safety glasses and face shield on your forehead.

2. Be sure regulator adjusting screws are turned out. The screw should turn freely.

3. Standing to one side, not directly in front of the regulator, open the oxygen cylinder valveslowly. Then open it all the way. Set the regulator at the correct working pressure. Open theoxygen blowpipe valve, and fine tune the operating pressure. Close the oxygen blowpipe valve.

4. Standing to one side, not directly in front of the regulator, open the acetylene cylinder valveslowly. Only open the tank valve ½ to ¾ of a turn. Set the regulator at the correct workingpressure. Open the acetylene blowpipe valve, and fine tune the operating pressure. Close theacetylene blowpipe valve.

(Continued)


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Acetylenehose

connection

Oxygenhose

connection

Acetylenecontrol valve

Oxygen andacetylene mixture

Oxygencontrol valve

Oxygen

Tip

Tip connectionto mixer

Torch body

Acetylene Mixer

FIGURE 2. Blowpipe detail.

TABLE 2 (Continued)

5. Put on gloves, and lower the goggles or face shield over your eyes.

6. With the friction lighter in your left hand at the tip of the blowpipe and the blowpipe in yourright hand, open the acetylene blowpipe valve, with your right thumb and forefinger, one-eighth to one-quarter turn. Strike the friction lighter, and adjust the acetylene level.

7. Adjust the acetylene by opening the blowpipe valve until the flame leaves the tip about ¼inch. Close the valve very slowly until the flame is pulled back to the end of the tip. Open thevalve slowly again, stopping just before the flame leaves the tip. This is the proper adjustmentfor most welding.

8. Open the oxygen blowpipe valve, and set the desired flame type.

Flames

There are three types of oxyacetylene

welding flames: neutral, oxidizing, and

carburizing. The neutral flame is usually

used for welding. A neutral flame is a

flame that will produce a smooth, shiny

bead of the best quality. Meanwhile, the

oxidizing flame is a flame caused by

an excessive amount of oxygen, which

produces a short white inner cone and a

short envelope flame. An oxidizing

flame will produce sparks that shower

the weld area with droplets of metal and

slag, leaving the weld zone weak and

porous. In contrast, the carburizing

flame is a flame caused by an excessive

amount of acetylene and has a long, blu-

ish outer flame. A carburizing flame will

cause the puddle to foam and boil, leav-

ing a brittle, porous, and scaly weld area.

The carburizing flame is used for hard-

surfacing.

TECHNIQUES

The techniques of fuel gas welding include setting the proper flame, preparing the pieces to

be welded, knowing the common weld types, holding and using the blowpipe and rod, and

completing the different weld types by using braze or fusion welding. Braze welding (formerly

referred to as bronze welding) referred to the use of a bronze filler rod. In braze welding, as


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Carburizing Flame

Oxidizing Flame

Neutral Flame

FIGURE 3. Flames.

the melting point of the filler rod is achieved, the metal surfaces are joined together. Fusion

welding allows for the base metal to be melted and mixed together; it forms a joining. Fusion

welding can be completed with or without a filler rod.

Preparing the Metal

Metal should be cleaned before any form of welding is conducted. The cleaning procedure

allows for the removal of oxides or any other form of impurities. Using mechanical means

(e.g., a wire brush, grinder, file,

sander, or steel wool) allows for

the removal of oxides, such as

rust. A chemical could be used to

remove any remaining impurities.

The edges of metals over 1/8

inch should be cut to form a V,

with approximately a 45-degree

angle to permit complete fusion

of the pieces. If the pieces are 3/8

inch or more in thickness, it is

usually desirable to cut a V on the

top and bottom sides of the two

pieces of metal being welded. The

pieces to be welded should be


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TABLE 3. Shutting Off Procedure for Welding or Cutting Torch

Correct Shut-Down Procedure

1. Close the acetylene blowpipe valve.

2. Close the oxygen blowpipe valve.

3. Close the acetylene tank valve.

4. Close the oxygen tank valve.

5. Open the acetylene blowpipe valve to drain the hose and to release all pressure from thehose and regulator.

6. Turn out the pressure-adjusting screw on the acetylene pressure regulator by turning itcounterclockwise.

7. Close the acetylene blowpipe valve.

8. Open the oxygen blowpipe valve to drain the hose and to release all pressure from the hoseand regulator.

9. Turn out the pressure adjusting screw on the oxygen pressure regulator by turning itcounterclockwise.

10. Close the oxygen blowpipe valve.

11. Wrap up the hoses, and put the welding accessories in their proper place.

FIGURE 4. Forming a V in preparation of fuel gas welding.

placed about 1/16 inch apart to provide for the expansion and contraction of the metals and to

permit the weld to penetrate deeply, through the bottom, if possible.

Types of Welds

The two most common weld types are the butt weld and the fillet weld. Types of welded

joints frequently used are the butt joint, tee joint, corner joint, lap joint, and edge joint. The

common welding positions are downhand, horizontal, vertical, and overhead. The downhand

weld is used most frequently and is the easiest weld to make.

Position of Equipment

The blowpipe is usually held in the same say as a hammer or a fishing pole when the opera-

tor is welding while standing. It is held in the same manner as a pencil when the operator is

welding while seated. The operator should hold the blowpipe in a comfortable way.

The recommended blowpipe position allows for the tip to be inclined at a 45-degree angle

to the welded surface point directly along the line of the weld. Hold the tip so the inner cone

of the flame is about 1/8 to 1/16 inch above the surface of the metal.

Before lighting the blowpipe, practice holding it and moving it in the motion used in weld-

ing. The blowpipe may be moved in a straight line, in a zigzag, or in a circular motion. The cir-

cular motion is most frequently used. Move the blowpipe in a series of connected ovals in a

left-to-right direction and along the line of welding. Advance each successive oval about 1/16

inch. Make the oval about 1/4 inch wide and 5/16 inch long.


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GROOVE JOINTS

FILLET JOINTS

Flat position

Horizontal position

Vertical position

Horizontal position

Vertical position

Overhead position

Overhead position

Flat position

Axis ofweld

Axisof

weld

Axisof

weld

Axisof

weldAxisof

weld

Axisof

weld

Axis ofweld

Axis of weld

FIGURE 5. Welding joints and positions.

Learning How to Form a Molten Puddle

To weld with oxyacetylene, learn how to melt the base metal and how to control the molten

puddle. Start the flame at the edge of the steel piece, and form a molten puddle about 1/4 inch

in diameter and about 1/8 inch from the edge of the piece of steel. The width of the puddle is

about twice the thickness of the metal.

After learning to control the molten puddle, learn how to make a bead. A welding rod is

added to the process. The rod melts as it is added to the molten metal. As it progresses across

the metal, it is called “making a bead.”

If you are right-handed, hold the welding rod in your left hand at a 45-degree angle so the

end of the rod will be within the outer envelope of the flame. Move the blowpipe in a circular

motion, and dip the rod into the center of the puddle each time the flame reaches the back of

the circle. Raise the rod out of the puddle slightly as the flame is passed toward the front to the

puddle, thus synchronizing the motions of the flame and the rod.

Maintain a molten puddle about 1/4 inch in diameter, and move the rod and blowpipe

slowly, straight ahead about 1/16 with each oval motion of the blowpipe. Raise the rod out of the

flame’s way to permit the flame to heat the metal ahead of the bead. Lower the rod so the

flame will melt it, causing the welding rod to flow into the molten puddle. The end of the

welding rod should touch the puddle on the downward stroke. The rod should not dip into

the puddle.

Fusion Welding

A fusion weld is the next step

after learning to make a bead.

Two pieces of metal are welded

together using a filler rod. Select

two pieces to be welded, and

space them so the edges of the

metal are 1/16 inch apart at one end

and approximately 1/8 inch apart at

the other. Make a tack weld at

each end of the pieces to hold

them together. Follow the same

procedure and motion used in

making a bead.

Braze Welding

Braze welding has some advantages over fusion welding. Brazing and soldering are con-

ducted at low temperatures, can be completed faster, show little damage to parts, can join dif-

ferent metals, and allow for easy disassembly.

Heat the base metal to a salmon red color. The bronze rod should not remain in the inner

cone of the flame. In addition, the inner cone of the flame should not stay in one spot of the


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Direction of Travel

ConeFiller Rod

Welding Torch Tip

Acetylene Feather

Molten Weld Metal

Solidified

Weld Metal

FIGURE 6. Fuel gas welding structure.

molten bronze because the intense

heat will burn the bronze. The

same technique and movement

used with fusion welding should

be followed.

SAFETY PRACTICES

The following safety practices

should be conducted at all times

when working with fuel gas weld-

ing.

1. To prevent oxygen and fuel

cylinders from being tipped

over accidentally, fasten

them securely in an upright

position with a chain or a

similar device before

removing the safety cap.

2. Keep oil and grease away from oxygen cylinders and equipment.

3. Check equipment connections periodically for any leaks by using the soapy water

method.

4. Check regulator gauge operation pressures carefully, and follow recommendations.

5. Clear the area of all combustible materials before lighting the torch.

6. Cover your eyes with welding goggles or a colored face shield, and put on gauntlet

welding gloves before lighting the torch. Wear clothes suitable for the work being done.

7. Stand to one side, not directly in front of the regulator, when opening the cylinder

valve.

8. Do not open the blowpipe valves more than ½ turn when lighting the torch.

9. Never use a match to light the torch.

10. Always use a spark igniter or a friction lighter to light a welding torch. When lighting a

torch, keep the tip facing downward and away from you.

11. Light the acetylene first, and add oxygen to the flame. Make no attempt to relight a

torch from hot metal.

12. Be sure that other workers are in the clear before relighting a torch.


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The correct position of a blowpipe and rod

when the rod is lowered.

FIGURE 7. Fuel gas welding position.

13. Do not walk with a lighted torch or lay down a lighted torch. Before you light the

torch, get into position for welding or cutting, and remove all obstacles between you

and the shut-off controls.

14. Before opening a cylinder valve, be sure the regulator valve is closed by turning it coun-

terclockwise until it is loose.

15. If a flashback should occur, turn off the torch immediately, close the cylinder valves,

and notify your instructor. A flashback has occurred when the flame disappears and

burns back inside of your equipment. There is a hissing, squealing sound. Smoke may

come out the torch tip, and the handle may become hot. If the torch is not turned off

promptly, fire may reach the hoses or the cylinder. Do not relight after a flashback until

the equipment has been inspected closely. The equipment may require repairs.

16. Never open the acetylene cylinder valve more than ½ to ¾ of a turn. Leave the T-han-

dle wrench in position at all times while welding. You should be able to turn off the

acetylene cylinder valve promptly in case of a fire.

17. Never do any welding on containers that may have held flammable substances.

18. When welding or cutting zinc or galvanized metals, make a special effort to avoid

breathing the fumes because they can make you feel ill.

19. Never use acetylene at a pressure greater than 15 psi. Follow the manufacturer’s recom-

mendations for the correct operating pressures for the metal being welded and for the

tip size being used.

20. Do not smoke or allow anyone else to smoke near the oxy-fuel gas welder.

21. Keep the flame and heat away from the cylinder, hoses, and people. Be alert for fires at

all times. Use the proper fire extinguisher or a fire blanket if necessary.

22. For most oxyacetylene welding, you will need a lens with shade No. 5.

23. Cylinders should not be stored near open fires, furnaces, or other heating devices or in

direct rays of the sun.

24. Keep cylinders away from electric wiring and away from the danger of striking an arc

on them with an electric welder.

25. Oxygen cylinders are equipped with a double seating valve. Open the valve all the way

to prevent oxygen from escaping around the valve stem.

26. Wear welding gloves to protect the hands against burns, sparks, and molten metal.

27. Wear flame-resistant clothing.

28. Low shoes are not recommended because sparks or slag may get into them.

29. Make certain that reverse flow-check valves and flash arrestors are installed on the oxy-

gen and acetylene lines.


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30. Be sure the cylinder valves are closed and the pressure is relieved from the hoses before

you leave the work area.

31. Remove regulators and replace protective caps before transporting cylinders.

32. Store oxygen cylinders away from fuel gas cylinders.

33. Never use oxygen as compressed air to dust clothing because clothing saturated with

pure oxygen is highly combustible.

34. Handle hot metal with pliers or tongs. Do not leave hot metal on the welding table

because unsuspecting people may touch it and may be burned.

Summary:

� Oxyacetylene welding is a process by which two pieces of metal are joined. Acety-lene and propane are commonly used fuel gases. Oxygen is used to support com-bustion. Cylinders, regulators, hoses, a blowpipe, and tips are common equipmentused in the set-up of fuel gas welding.

Safety is extremely important during fuel gas welding. Materials used can damageeyes, skin, hands, and feet. Therefore, protective clothing and proper proceduresmust be followed and conducted during shop exercises.

Following proper procedures when setting up the fuel gas welding equipmentshould help avoid gas leaks and minimize accidents. A common way to test for leaksis to use soapy water around valves and connections. If a bubble appears, a leak hasbeen detected.

Using proper techniques (e.g., achieving a desired neutral flame) will ensure qualitywelding. Other techniques include cleaning metal surfaces, preparing edges, identi-fying weld types, and positioning of equipment. The final steps in fuel gas weldingare learning how to control the molten puddle and making a bead.

Checking Your Knowledge:

� 1. What are three advantages of acetylene?

2. What are the key safety factors when setting up cylinders?

3. What is a flashback, and what safety practices should be followed immediately?

4. What are the procedures for fuel gas welding equipment set-up?

5. What are the differences between neutral, oxidizing, and carburizing flames?


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Expanding Your Knowledge:

� Practice fuel gas welding (FGW) processes and techniques. First, view the followingvideo: http://www.youtube.com/watch?v=YjwsKjqWiS8. Practice forming a beadon a piece of steel (1/8“ × 2" × 2"). Then watch the following video:http://www.youtube.com/watch?v=mMADiAMfe00&feature=related. Prepare ablowpipe/torch, two steel pieces (16 gauge × 11/2” × 6), flux, and a 1/16-inch weldingrod. Butt weld the two pieces by using the filler rod.

Web Links:

� Welding Technology Machines

http://www.welding-technology-machines.info/index.htm

Brazing/Welding Procedures and Techniques

http://www.brazing.com/techguide/procedureMain.asp

Braze Welding

http://www.tandtlanco.com/index_files/Page4045.htm


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http://www.youtube.com/watch?v=YjwsKjqWiS8

http://www.youtube.com/watch?v=mMADiAMfe00&feature=related

http://www.welding-technology-machines.info/index.htm

http://www.brazing.com/techguide/procedureMain.asp

http://www.tandtlanco.com/index_files/Page4045.htm

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